As others have pointed out you can make the cutout any size you want as long as you adjust the distance you hold the frame from your eye appropriately. I find the actual film size most appropriate. But I use 96 x 120 mm, which is a bit smaller than 4 x 5 inches, because that is very close to the actual exposed film area for sheet film in a holder.

I also suggest putting centering marks on all for sides of the frame, and then adding marks indicating the distances up, down or sideways your camera can provide in movements. That way you are less likely to be surprised about what is actually a feasible framing after you set up your camera.

Frames like this give you a pretty good idea of what you will see for normal or long lenses, but they can mislead you for shorter focal length lenses. They will show you geometrically what is in the frame, but with your eye so close to it, it is hard to really see what is there.